This invention relates to a sewing machine for automatically forming a stitch pattern on a workpiece, by relatively moving a needle and the workpiece based on pattern data stored in advance in memory means, with a plurality of stitches formed thereon in response to vertical movement of the needle. More particularly it relates to a sewing machine which is provided with a device for preventing an impact or interference between the needle and the workpiece. As a sewing machine including an impact preventing device in this sense, U.S. Pat. No. 4,002,128 can be cited, wherein a workholder which is so mounted as to be movable, in relation to a vertically movable needle, in a plane defined by X and Y axes is automatically halted by a moving amount restricting device for the workholder when the workholder goes beyond a predetermined limit in the direction of X and Y axes within which the workholder is allowed to move. It is true indeed that an impact matter between the needle and the workholder which may happen in an actual pattern forming operation can be prevented in this device.
Assume a case, however, a given number of blocks of unit pattern information are selected from a memory means which stores in advance plural blocks of unit pattern information for forming a combination pattern on a workpiece held on a workholder based on the selected unit pattern information, or a case wherein a larger size than that corresponding to the prestored pattern information in the memory means is set for realizing the stitch pattern of the set size on a workpiece held on a workholder. If the stitch pattern according to the selected blocks of unit pattern information or the set large size turns out to be larger, i.e., to exceed in its size the movable area allowed to the workholder, the relative movement of the workholder to the needle is halted in the course of pattern formation. The impact between the needle and the workholder can be prevented, in the cited disclosure, but the operator can not be aware of the fact that the selected stitch pattern or the stitch pattern based on the set size becomes larger than the movable area of the workholder before the stitch pattern is actually formed. Therefore, the operator may be obliged to, when she forms a stitch pattern on the workpiece after the selection operation of the unit pattern information or the setting operation of the size, interrupt the stitch forming operation halfway so as to remove the already formed portion of the stitch pattern from the workpiece, which needs disadvantageously a lot of time for her. Because of difficulty of removing the needless stitches already formed, the errored workpieces have been in many cases thrown away so far as commercially worthless.
Moreover, the impact preventing device in the earlier mentioned prior art for the workholder was what restricts the movement amount along the X and Y axes respectively, which naturally limited the area in question, i.e., the movable area for the workholder to be quadrangular in shape. A circularly shaped movable area, for example, preferred to a workholder of annular shape was impossible in the prior art.